This invention relates to a lubrication system for drum-type brakes and more particularly to an improved system for lubricating the actuating mechanism for a cam actuated drum-type brake.
U.S. Pat. No. 4,380,277, entitled "Automatic Slack Adjuster For Vehicle Shoe-Drum Brakes", issued Apr. 19, 1983 in the name of Brian Ingram et al and assigned to the assignee of this application, shows a very popular and successful type of brake. In this brake, a pair of brake shoes are operated by means of a cam that is rotatably journaled relative to a backing plate and which operate a pair of struts which, in turn, transfers thrust to the brake shoes through a pair of adjustable tappet assemblies. With this type of mechanism, it has been the practice to provide a grease fitting for lubricating the camshaft. The cam itself and the associated actuating mechanism is, however, lubricated by removing a cover plate of the actuator housing and packing this mechanism with grease. Although such an arrangement is satisfactory, the removal of the cover plate for replacing the lubricant gives rise to the possibility of contamination. When the cover plate is removed, foreign material may enter into the actuator housing and damage could result. Furthermore, when the cover plate is removed for lubrication purposes, there is always the danger that the internal components may be removed and improperly reassembled.
It is, therefore, a principle object of this invention to provide an improved lubricating system for the actuating mechanism of a drum type brake.
It is a further object of this invention to provide an improved lubricating system for a cam actuated brake wherein the cam, associated actuating mechanism and camshaft can all be lubricated at the same time without necessitating disassembly.
It is a still further object of this invention to provide a lubricating system of the type aforedescribed in which an automatic adjusting mechanism is also lubricated at the same time the remaining components are lubricated and without necessitating opening of the system.
In connection with many types of brakes that embody cam actuators and automatic adjusting mechanism, the internal volume of the actuator hosuing will vary during use. For example, in the brake of the type shown in aforenoted U.S. Pat. No. 4,380,277, as the brakes become worn, the adjusting tappets are extended and may displace some of the volume within the actuator housing. In addition, when the brake is actuated, the internal volume of the housing varies as the tappets slide from their retracted to their extended position. Such changes in volume can cause pressure differences within the housing which can either force lubricant from the housing to escape, if the volume decreases, or air to enter the housing if the effective volume increases. Neither condition is desirable.
It is, therefore, a still further object of this invention to provide an arrangement that ensures against the loss of lubricant or the ingress of air during changes in effective volume of the actuator housing of a brake of this type.